Effect of organic and inorganic sources of nitrogen on growth, seed yield and oil content of sunflower grown in highly weathered soils in Morogoro - Tanzania

Sunflower contributes about 40% of total national cooking oil requirement, ranking as one of the most important cooking oil with very high nutritional value in Tanzania. However, its production per unit area ranges between 800 to 1100 kg/ha, the average which is far below the potential production of 1200 to 2000kg/ha in most African countries. The low sunflower productivity is partly attributed by low soil fertility. A study was conducted to determine the effect of inorganic nitrogen fertiliser and farmyard manure on growth, yield and oil content of sunflower. A field experiment was set up at Sokoine University of Agriculture soil science experimental site during the short rains of November 2013. The treatments consisted of a control (no fertiliser, no farmyard manure), 2t farmyard manure (FYM)/ha, 5 t FYM/ha, 10 t FYM/ha, 20kg N/ha, 40kg N/ha, 60kg N/ha, 2 t FYM/ha + 20 kg N/ha, 5 t FYM/ha + 40 kg N/ha and 10 t FYM/ha + 60 kg N/ha. These treatments were laid out in a randomized complete block design and replicated three times. Data on plant biomass, seed yield, 1000- seed weight and oil content were collected and subjected to analysis of variance. Application of 40 kg N/ha, 60 kg N/ha, 10 t FYM/ha and combined farmyard manure and N fertilizer treatments showed significantly higher dry matter yield than the control. Application of 10 t FYM/ha + 60 kg N/ha significantly increased seed yield by 190.7% compared to the control. Plots supplied with 40 kg N/ha, 10 t FYM/ha, 2 t FYM/ha + 20 kg N/ha and 10 t FYM/ha + 60 kg N/ha had significantly higher 1000-seed weights than the control. Among all the treatments, oil content ranged from 33.7 to 47.4%. Application of 10 t FYM/ha significantly increased the oil content by 18.3% relative to the control. Highest sunflower yield components were recorded from plots treated with 10 t FYM/ha and partly with 10 t FYM/ha +60 kg N ha.